Electrical discharge machining has grown to be the preferred machining technique for a variety of production machining procedures, including the production of molds, dies, and complex three-dimensional workpieces, particularly those of difficult to machine materials. The efficiency and accuracy of the technique have had continuous attention and upgrading, and have increased substantially since inception.
The broad acceptance of electrical discharge machining in the context of complex shapes and difficult to work materials has not led to the still broader application to easier shapes and easier materials despite substantial theoretical advantages. In particular, the excessive levels of electrode wear pose economic limits on the applicability of electrical discharge machining, so that only the most demanding operating justify and warrant the expense and inconvenience of these procedures.
High rates of electrode wear are to a large extent inherent in the electrical discharge machining operation itself, although through the years a number of techniques have been developed or have evolved to reduce the rate of electrode wear in relation to metal removal on the workpiece. These steps have, however, met a limit. If electrical discharge machining parameters are chosen to keep electrode wear to the minimal levels attainable, often referred to in the art by the misnomer "zero wear conditions" in a collective conspiracy of wishful thinking, the electrode will still have one part wear for each one hundred parts of stock removal from the workpiece. Electrode wear is not ordinarily uniform
In the usual context, it is not uncommon to require more than one electrode for each workpiece, or in some few cases, a few workpieces can be machined before the elecrode is so far out of tolerance as to be unusable.
Becuase electrode wear is the single greatest limitation of electrical discharge machining, operational parameters are normally set to "no wear" conditions to conserve the electrode as much as possible. While the functional life of the electrode can be prolonged by such techniques, they come at the expense of the time of the electrical discharge machining operation.
The major benefit of all this is the relative ease of making the graphite electrodes by conventional machining techniques. In fact, it is the ease of machining, along with the excellent electrical and thermal properties which have led to the emergence of graphite electrodes as the best electrical discharge machining cutting tools, to the practical exclusion of other electrode materials, such as a variety of metals.
The usual procedures of machining an electrode are no different from any other machining procedure, and are substantially the same as would be required to make a workpiece, except that the graphite is rather easy to work and the electrode configuration is a mirror image of the desired workpiece to be formed by electrical discharge machining. As a result, the electrode represents a considerable investment. Either machining new electrodes or re-machining of used electrodes to re-establish dimensions lost and worn away by use represent significant time and cost. While the ease of machining graphite produces a significant savings, the extent of the benefit is primarily dependent on the workpiece material. The more difficult the workpiece is to machine by conventional machining operations, the greater the savings of electrical discharge machining operations.
Given the considerable time and cost invested in the making of electrical discharge machining electrodes, it is easy to understand the willingness of the art to tolerate the slow and less than optimum requirements of "no wear" conditions during the electrical discharge machining operation. If only "no wear" meant that there was, in fact, very litte wear, such a result would be tolerable, but the one percent wear rate is in practice quite substantial and, given any alternative, quite unacceptable.